A non-cytotoxic lymphokine (TMIF) that inhibits the migration of a variety of tumor cells in vitro has been described previously. This lymphocyte-derived mediator is distinct from other migration inhibitory lymphokines that affect inflammatory cells. The purpose of the present study is to further characterize TMIF from a variety of in vitro and in vivo sources and to extend observations regarding cells capable of responding to it. Specifically, cultured tumor cell lines will be examined, as well as tumors propagated in vitro in ascitic form. In addition, cells will be obtained from dissociated solid tumors, and their capacity to respond to TMIF will be investigated. We will also continue to evaluate the specificity of TMIF for neoplastic cells. In work performed to date, it has been demonstrated that TMIF has a variety of important biological properties in addition to its effect on migration. It can interfere with endothelial cell-tumor cell binding, enhance CTL-mediated cytotoxicity and exert cytostatic effects on tumor cells in vitro. These results provide additional leads as to potential clinical applications for this new lymphokine.